expressjs 源码 为什么用mixin拓展app， 而不是像下面用Object.create一样拓展req一样拓展app

Question

function createApplication() {
  var app = function(req, res, next) {
    app.handle(req, res, next);
  };

  mixin(app, EventEmitter.prototype, false);
  mixin(app, proto, false);

  // expose the prototype that will get set on requests
  app.request = Object.create(req, {
    app: { configurable: true, enumerable: true, writable: true, value: app }
  })

  // expose the prototype that will get set on responses
  app.response = Object.create(res, {
    app: { configurable: true, enumerable: true, writable: true, value: app }
  })

  app.init();
  return app;
}

代码Github页面地址点击这里

Answer 1

mixin不会改变目标对象的原型，会在原有对象基础上增加（或者说混入）新的属性，而Object.create是创建一个指定原型和若干属性的新对象。